The Mysterious Sacroiliac Joint

Low back pain (LBP) can arise from a number of structures that comprise the lower back like the intervertebral disk, the facet joints, the muscles and/or tendon attachments, the ligaments that hold bone to bone, the hip, and the sacroiliac joint (SIJ). Though several of these can generate pain simultaneously, the focus of this month will center on the SIJ.

The role of the SIJ is quite unique, as it has a big job: it is the transition point between the flexible axial skeleton (our spine) and the pelvis, below which are the lower extremities or legs. The pelvis supports the weight of the torso, which usually accounts for about two-thirds of our body weight. The SIJ is shaped at an oblique angle that diverges or opens at the front and converges inwards at the back of the joint in order to support the weight on top of it. Because the sacrum/tailbone is “V” shaped, it fits like a wedge and is held together with very strong ligaments, making it an inflexible but sturdy joint.

Making a diagnosis of SIJ syndrome or identifying it as a pain generator can be a challenge. Your chiropractor may depend on several types of examinations in order to arrive at an SIJ syndrome diagnosis, such as palpation looking for pain directly over the SIJ; compression tests of the pelvis; front-to-back hip movements to stretch the joint; and imaging, such as x-ray, CT scans, and MRI.

Since the SIJ is NOT a flat and smooth oblique joint, x-ray has many limitations. However, the pubic bone called the “symphysis pubis” (SP), which is located in the front of the pelvis, can be easily seen on x-ray. Because the pelvis is a ring-like structure, an SP that is out of alignment may indicate SIJ dysfunction.

In a recent study, two independent orthopedic surgeons analyzed the x-rays of 20 consecutive patients (17 women and 3 men) with proven SIJ dysfunction and LBP (confirmed by SIJ injection testing), which resulted in the findings of osteoarthritic degeneration and subluxation (misalignment) in 18 of the 20 subjects.

When they assessed the SP in 20 non-SIJ LBP control subjects (16 women and 4 men), 7 had abnormal SP findings (35%) versus 18 of 20 with SIJ-LBP mentioned above (90%). A review of the patients’ past radiology reports found that only three reports mentioned this in the SIJ-LBP group and none reported this in the control group. The authors concluded that SP findings are underreported by radiologists, and because SP is much easier to “read” or assess than the SIJ itself, it NEEDS to be looked at!